Impulse recording optical system



Feb. 17, 1948. J. A. MAURER, JR

IIPULSE RECORDING OPTICAL SY S'I'BI Original Filed Dec. 4, 1944 2 Sheets-Sheet -1 FIG. I

FIG.2

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mmvron: JOI-N A. MAURER, JR.

AGENT Feb. 17, 1948. j .LA. MAURER, JR 2,436,148

IMPULSE RECORDING OPTICAL SYSTBI I Original Filed Dec. 4, 1944 2 Shoots-Sheet 2 FIG. 4

nvvmvrox: JOHN A. MAURER,JR. "figZW AGENT Patented Feb. 17 1948 2.438.148 IMPULSE RECORDINQ OPTICAL SYSTEM John A. Maurer. Jr., New York, N. 1L. minor to J. A, Maurer, 1nc., Lon corporation oi New York Application December 4, 1944,

which is a division of application Serial g Island City, N. 2., a

SerlaiNo. 566,459, No.

August 2, 1940. Divided and this application July 11, 1946, Serial No. 882,725

3 Claims.

This invention relates to optical systems for the photographic recording of electrical impulses on a moving him such as are used in sound recording, picture transmission, and the like, and this application is a division 01' my application Serial No. 566,459, flied December 4, 1944, which, in turn, is a division oi my application Serial No. 349.515, filed August 2, 1940; applications Serial No. 349,515 and Serial No. 566,459 being also assigned to J. A. Maurer. Inc., a corporation or New York, application Serial No. 349,515-now being abandoned, and application Serial No. 566,459 now being Patent No. 2,426,366, granted Aug. 26, 1947.

More particularly, the invention relates to optical systems of the class referred to above wherein a small mirror vibrated by an oscillograph galvanometer, or a similar device for translating electrical impulses into mechanical vibrations, modulates a light beam in accordance with the electrical impulses to be recorded. The mirror oscillograph recording optical systems known heretofore, however, have the disadvantage that the light flux from therecording light source,- such as the filament oi an incandescent lamp, is not efilciently utilized therein. This unfavorable condition is due to the fact that the aperture of the oscillograph mirror is the limiting aperture in the two co-ordinate planes of the known optical systems, and that it cannot be enlarged yo d a ce ta n degree since the physical size of the mirror must 'be'comparatively small in order to avoid distortions due to its mass. For

a given light source, therefore, the amount of light flux reaching the moving film is unduly limited in those optical systems, and this limitation makes itself particularly felt when filters are used at some position in the optical system, for example, for selecting light rays of a certain wave length, or for other purposes.

Another drawback of the known mirror oscillograph recording optical systems is that a portion of the light flux from the recording light source is not eil'ectively prevented therein from falling on parts other than the oscillograph mirror, or on the structure housing the optical system. This portion oi the light flux is to some extent reflected diffusely, thus forming stray light even though the surfaces on which it is incident may be black. Such stray light is objectionable because it may cause an additional exposure oi the moving him, which should be exposed on'y to light flux modulated by the oscillograph mirror.

It is, therefore, an object of the present invention to provide a mirror oscillograph recording optical system which is highly eiilcient as regards the utilization of the light flux from the recording light source. I

- Another oblect of the invention is the provision of such an optical system whose limiting aperture can, in one of its co-ordinate planes, be made much larger than the aperture of the oscillograph mirror.

Another object of the invention is the provision of-such anoptlcal system wherein the formation of stray light is reduced to a negligible amount.

Another object of the invention is the provision of such an optical system which is particularly satisfactory as regards ease of manufacture and convenience of adjustment.

More specifically, however, it is an object of the invention to provide a mirror osciilograph recording optical system which embodies the teaturcs recited above and which may be built at materially reduced cost.

A further object 0! the invention is the provision of such an.'optica l system which may be built-with small physical size and great c'o mpactness.

Still other objects of the invention include those which are hereinafter stated or apparent, or which are incidental to the invention.

in the optical system according to the invention, the oscillograpn mirror is adapted to vibrate about a horizontal axis while the film moves past the recording point in a substantially vertical direction, the recording point beingthe point at which the optical axis of the system strikes the fim. The optical system also has means for forming a light spot of vertically graded light flux. Further means are provided in the optical system when effect an imagery of this light spot in such a manner that it is conjugate to the recording point in both the vertical and horizontal planes of the optical system. Otherwise, however, the imagery of the light spot is diilerent in the two co-ordinate planes. In the vertical plane, the light spot is first imaged at a horizontal silt by imaging means acting in the vertical plane and then at the recording point by imaging means acting in only the vertical plane, the horizontal slit being placed between the oscillograph mirror and the recording point. In the hOIlZOi'ltal plane, on the other hand, an intermediate image of the light spot is formed substantially on the mirror by first imaging means which act in only the horizontal plane, and the intermediate imageis imaged at the recording point by second imaging means which likewise act in only the horizontal plane. By virtue'oi this arrangement, the mirror is substantially at a common focus of two imaging means whichact in only the plane containing its axis of vibration. and the limiting aperture in the horirontal" plane is the aperture of the second imaging means. The aperture of the secondlmaging means, however,

, can be made as much as five times as large as the aperture oi the osciilograph mirror.

intermediate image is formed substantially on the oscillograph mirror as has been explained hereinabove. At the same time, an image of the light source is formed substantially on the mirror by the action of a condenser lens in the vertical plane. In this manner, substantially all the light flux entering the optical system through the opening is controlled by the oscillograph mirror whereby the formation'of stray light is reduced to a negligible amount. v

The cost of buildingthe optical system according to the invention, finally, may be materially reduced by substituting for the above mentioned first and second imaging means a single imaging means which likewise acts in only the horizontal plane. To that end, the light beam proceeding through the optical system is made to strike the oscillograph mirror at an angle which is so small that the single imaging mean can be traversed by both the incident and reflected P r 01' he light beam. The single imaging means then forms the intermediate image of the light spot substantially on the mirror and. simultaneously, images the intermediate image at the recordin point. The angle at which the light beam strikes the mir... ror, is made sufllciently small preferably by folding the incident part of the light beam whereby, at the same time, a' very compact mechanical structure is obtained for the optical system.

In the foregoing brief explanation of the state of the art and summary of the invention, and throughout the present specification, the term "co-ordinate planes" designates two planes at right angles to each other whose line of intersection is the optical axis of the system. The horizontal plane is the co-ordlnate plane which contains the axis of the oscillograph mirror and the slit, while the vertical plane is the co-ordinate plane at right anglesto the horizontal plane. The plane of the slit, finally, is the plane which contains the slit, and is at right angles to both the vertical and horizontal planes.

In the present specification, the terms "vertical and horizontal thus are not used in any absolute sense but merely in order to distinguish between two planes, or directions. at right angles to one another. and choice between those terms ha been determined solely by convenience in description and illustration.

The invention willbe better understood when the following description is considered with the accompanying drawings of certain presently preferred embodiments thereof, and its scope will be pointed out in the appended claims.

In thedrawings: I

Fig. 1 is a diagrammatic perspective view of an optical system embodying the invention,

Fig. 2 is a diagrammatic longitudinal section in the vertical plane oi the optical system shown in Fig. 1, the optical axis being repr sented as a straight line and an oscillograph mirror as an aperture,

Fig. 3 is a corresponding section in the horizontal plane,

Fig. 4 is an elevation of a part of the optical system of Figs. 1 to 3, and

Fig,- 5 is a diagrammatic longitudinal section in the vertical plane of a modification in which two cylindrical lenses shown in Figs.l to 3 have' been replaced by a single cylindrical lens.

Referring first to Figs. 1 to 3, these figures show. by way of example, a variable area recording optical system which embodies the invention. The optical system has a light source such as the filament ill of an incandescent lamp ii. light flux from lamp filament i0 uniformly illuminates a triangular opening IS in a screen l4 so that a uniformly illuminated triangular light spot is formed at screen M. The light beam defined by lamp filament ill and opening i3 proceed through the optical system and is deflected bythe'mirror ll of an oscillograph galvanometer (not shown) or similar device for translating electrical impulses into mechanical vibrations. It thus has a part which is incident from opening i3 upon mirror i7, and a part which is reflected from mirror i1 towards the recording point 21. Recording point 27 is the point at which th optical axis of the system strikes the film 23, and film 23 moves past recording point T5 in a substantially vertical direction as indicated by the arrow 29.

More particularly, opening i3 is an isosceles triangle whose base extends horizontally, and mirror H is adapted to vibrate about an axis 'i8-i8 which likewise extends horizontally. Furtween screen it and mirror H. In front of mirror i! there is placed a second spherical lens i9 which acts on the reflected as well as the incident part of the light beam proceeding through the optical system. A second cylindrical lens 40 which alsohas its cylinder axis vertical, is placed between mirror I! and screen 22, while a third cylindrical lens iii has its cylinder axis horizontal and is placed between screen '22 and recording point 21.

These five imaging means have focal lengths relative to the other parts of .the optical system as follows (see Figs. 2 and 3):

Spherical lens i2 has one of its conjugate foci at lamp filament it, and the other substantially at mirror I], that is, either on mirror ii or at a one of its conjugate incl at opening it, and the other substantially at mirror i1 so that an intermediate lmage of opening is is formed substantially on mirror i'l. Spherical lens i9 has one of its conjugate focl at opening i 3, andthe other at slit 2!. Cylindrical lens Ell has one of its conjugate incl at theintermediate image of opening l3. and the other at recording point 2'9. Cylindrical lens 4i, finally, .has one of its conjugate tool at slit 2i, and the other at recording point 21.

By virtue of the arrangement described herein.- above of its various parts, the following imagery is performed in the optical system of Figs. 1 to 3: In the vertical plane (Fig. 2), spherical lens is forms an image of the uniformly illuminated opening IS in the plane of the horizontal slit 2i. This image of opening i3 moves vertically across The" Cylindrical lens i5 has 4 termediate image of 'slit II when mirror ll vibrates about the horizontal axis i8--i8; As much of slit II as is illuminated by the image of opening I3, is imaged at recording point 21 by cylindrical lens 4|.

' There thus is formed at recording point 21 a tinct horizontal boundaries. Likewise in the vertical plane. spherical lens I! forms an image of lamp filament l substantially on mirror 11, thereby filling mirror I! with light and also aiding in the uniform illumination of opening i3 by lamp filament i0.

- In the horizontal lens I! forms substantially on mirror I! the inopening l3, and an image of the intermediate image'is formed by cylindrical lens 40 at recording point 21. By virtue of this successive imagery of opening I: in the horizontal plane, the horizontal line image at recording point 21 has, in addition to its sharp and distincthorizontal boundaries, also sharply defined ends; f

Lenses 12 and [9 are spherical and hence have power in the horizontal as well as in the vertical plane. But their actions in the horizontal plane can be disregarded for the following reasons:

On account of its position and relative focal length, spherical lens I! tends to image lamp filament lil substantially on mirror I! also in the horizontal plane, The action, however. of cylindrical lens i5 interferes with this imagery to such an extent that it become immaterial for attaining the objects of the present invention.

On the other hand, the power of spherical lens.

la in the horizontal plane has no effect upon the actions of cylindrical lenses l5 and ill on account of the proximity of spherical lens i9 to mirror I! which is, in the horizontal plane, substantially at a-common focus of cylindrical lenses i8 and 40. No actions, therefore, of spherical lenses i2 and i8 have been indicated in Fig. 3.

- Cylindrical lenses i5 and 40, in-their'turn. do

not interfere with the imagery in the vertical plane since they have their cylinder axes vertical,

and' hence act in only thehorizontal plane. Correspondingly,,cylindrical lens 4i does not interfere' with the imagery in the horizontal plane since it has its cylinder axis horizontal, and hence acts in only the vertical plane.

The imagery performed in the vertical and horizontal plancs'of' the optical system of Figs. 1 to 3 thus brings it about that recording point 21 is conjugate to opening it in both co-ordinate planes. In the vertical plane, horizontal slit 2h is, with respect to spherical lens [8, conjugate to a horizontal line through opening i 3, for example, the broken line a-a shown in Fig. 4. Since, furthermore, recording point 21 is in the vertical plane conjugate to slit 2i with respect to cylindrical lens I, it is also conjugate to line aa, The line image at recording point 2'! hence is an plane (Fig. 3), cylindrical line,through opening 13 to which recording point 21 is conjugate, is determined by the angle or inclination of mirror i1. Normally, mirror I! is adjusted so that at its rest position, that is, when no electrical impulses are applied to the oscillograph galvanometer on which it is mounted. recording point 21 is conjugate to line H, which line passes through opening i3 halfway between its tip and its base. When then the electrical impulses to be recorded are applied in known manner to the oscillograph galvanometer, mirror ll vibrates in accordance therewith about the horizontal axis l8-i8 and in such a manner that, when the amplitude of its vibration is a maximum. recording point 21 is conjugate to line 12-22 at the one extreme of its motion and to line c--c at the other extreme thereof. The length of the line image at recording point 21 hence varies in accordance with the vibration of mirror I! and, therefore, the electrical impulses to be recorded. A variable area track 28 thus is produced-on film 23 as it moves past recording point 21.

As has been explained hereinabove, recording point 21 is conjugate to opening i3 or, more exactly. to a horizontal line through opening l3, in the horizontal aswell as the vertical plane of the optical system of Figs. 1 to 3. The imagery, however, which results in this condition, is diilerent 11' and images opening l3 immediately at slit 2!.

the light flux from opening is isin the vertical plane-diffused at mirror IT. This is necessary because the vertical plane is the plane through which the light beam is deflected when mirror I! vibrates'about the horizontal axis i8-- i 8, thereby selecting, in co-operation with the horizontal slit 2i; horizontal lines through opening I! which beimage of line H as far as its vertical extension,

0) width, is concerned, and it is, according to a well known property of conjugates, made up of the light flux emanating from line H. Moreover, this light flux is brought to a focus at recording point 2! also in the horizontal plane, namely--as has been explained hereinabove-by the successive imaging actions of cylindrical lenses i5 and 40. The line image at recording point 21 hence is. an image of line a-a also as far as its horizontal extension, or length, is concerned. When, therefore, the horizontal line through opening I! is short-as is, for example,

come conjugate to recording point 21.

In the horizontal plane, on the other hand, an intermediate image or opening I: is formed substantially on mirror 11 by cylindrical lens iii, and this intermediate image is imaged at recording point-21 by cylindrical-lens '40. Since cylindrical lenses i5 and 40 act in only the horizontal plane, mirror I! is substantially at a common focus of two imaging means which act in onlv the plane containing its axis of vibration i8-i8. For any given angle of inclination of mirror i'l. therefore, the amount of light flux from opening i3 which is acted upon by cylindrical lens ill, is limited by the aperture of this lens rather than the aperture of mirror I1. The aperture of cylindrical lens 40, however, may be made as much as live times as large as the aperture which it is practical to give to mirror I].

The result thus obtained by means of the novel imagery embodied, by way of example, in the mirror oscillograph recording optical system of Figs. 1 to 3 represents a marked advance over the prior art. In the known optical systems, the light flux from the entrance position corresponding to opening I 3 is diffused at the oscillograph mirror in the two co-ordinate planes so that the mirror aperture is the limiting aperture of the optical systems also in the co-ordinate plane which con- 7 tains the mirror axis. Since the physical size of the oscillograph mirror must be comparatively small in order to avoid distortions due to its mass, the above condition has been a serious obstacle to an eflicient utilization of the light fiux in the prior art optical systems. The advantage gained in this respect. by the imagery according to the invention is considerable because, as is well known to those skilled in the art, the emciency with which the light flux from a given light source is utilized in an optical system, is approximately proportional to the product of the limiting apertures in the two co-ordinate planes of the optical system.

Another advantage of having, in the optical system of Figs. 1 to 3, mirror ll substantially at a common focus of two imaging means which act in only the horizontal plane.is that small deviations of mirror ll about a vertical axis have a negligible effect on the imagery in the horizontal plane. Mirror ll need therefore be accurately adjusted only about the horizontal axis 18-18. This greatly increases the ease of adjustment of the optical system, and is particularly im :ortant when it is necessary to replace the oscillograph galvanometer on which mirror I1 is mounted.

A'further advantage of the imagery performed in the optical system of Figs. 1.to 3 resides in the fact that there is formed substantially onmirror l'i an image of lamp filament ill by the action of spherical lens II in the vertical plane, and simultaneously the intermediate image of opening i3 by the action of cylindrical lens IS in the horizontal plane. It thus is possible so to control the light flux entering the optical system through opening l3 that it is all incident within the working aperture of mirror l'l. This result is best obtained when the focal length of spherical lens I? and the position of lamp H are chosen so that the image of lamp filament ID has a vertical dimension no larger than that of mirror ill, and when the focal length of cylindrical lens l5 and the position of screen I4 are chosen so that the largest horizontal dimension of the intermediate image is no larger than the horizontal dimension of mirror ll. If these conditions are fulfilled, all the light flux passing through open-' ing I3 is subject to control by mirror ll, whereby the formation of stray light in the optical system is reduced to a negligible amount.

The employment, finally, of cylindrical lens 4i in the portion of the optical system between screen 22 and recording point 2'! has certain inherent advantages: Cylindrical lens 4| may have a short focal length so that the optical system may be built with small physical size. Moreover,

a cylindrical lens of short focal length is less expensive than a spherical lens, or lens system. well enough corrected to form, over the same distance, an equally sharp line image. The optical system of Figs. 1 to 3 may hence be built with greater compactness and at less cost than the mirror oscillograph recording optical systems known heretofore.

The costof building an optical system according to the invention may be further reduced by making the light beam defined by lamp filament l6 and opening 13 strike mirror ll at a small angle. It then is possible to substitute a single cylindrical lens H for the two cylindrical lenses I5 and MI of Figs. 1 to 3. Like cylindrical lenses l5 and 40, cylindrical lens II has its cylinder axis verticahand it is placed so as to be traversed by the reflected as well as the incident part of the light beam deflected by mirror ll. The relative focal length of cylindrical lens H is so chosen that opening. I! and a position on. orclose to, mirror H are conjugate with respect to cylindrical lens ii on the incident part, and this position and recording point 21 are'conjugate withv respect to cylindrical lens 1| on the reflected part of the light beam. In this manner, cylindrical lens Ii forms the intermediate image of opening 43 substantially on mirror I! and, simultaneously, images the intermediate image at recording point One way of making the angle at which the light beam strikes mirror ll, suillciently small consists in considerably lengthening the optical system mechanically. But, while such an arrangement materially reduces the cost or building the optical system on account of the replacement of two cylindrical lenses by a single cylindrical lens, it I sacrifices the compactness of its mechanical structure. The latter disadvantage is overcome in and a very compact mechanical design of the optical system is provided by, the arrangement shown in Fig. 5 by way of example. In this arrangement, a reflecting prism ill is placed between the screen it and the mirror ll whereby the inci-.

dent part of the light beam is folded so that it strikes mirror ill at a small angle, and cylindrical lens I i is traversed by both the incident and reflected parts of the light beam. In place of prism 10 there may be employed other suitable beam folding means such as mirrors, or the like.

It will be understood by those skilled in the art that the optical system of Fig. 5 is susceptible to most of the modifications shown and described in Patent No. 2,426,366 with respect to the optical system of Figs. 1 to 3. For variable arearccording, the various openings, or pairs of openings,

' shown in Figs. 5 to 10a of Patent No. 2,426,366

may be substituted for the opening it in the screen it also in the optical system of Fig. 5 so as to form at screen iii-in conjunction with lamp filament l6 and condenser lens 12-9. uniformly illuminated light spot whose horizontal extension varies in a vertical direction, or a pair of such light spots.

For variable density recording, there may be employed in the screen id a rectangular opening in conjunction with either a penumbra stop or a light shading member as shown in Figs. 11 and 12, respectively, of Patent No. 2,426,366. The light spot formed at screen Mthen is of uniform horizontal extension and vertically varying illumination, but the light fiux emanating from it is vertically graded as in the case of the aforementioned openings whose horizontal extension varies in a vertical direction.

Furthermore, also in the optical system of Fig. 5, spherical condenser lens i2 and spherical drical lens ll should preferably be well corrected for spherical and chromatic aberration, and for coma, for the reasons set forth in Patent No. 2,426,366.

What is claimed is: 1. In an impulse recording optical system, the combination of light beam defining means which include means for forming a light spot of vertically graded light flux; a recording point past which a film may move in a substantially vertical direction: a mirror adapted to vibrate about a horizontal axis, said light beam being deflected by said mirror so as to have a part which is incident from said light spot upon said mirror, and a part which is reflected from said mirror towards said recording point; and a cylindrical lens placed between said light spot and said mirror and between said mirror and said recording point, said cylindrical lens having its cylinder axis vertical and being traversed by said incident and reflected parts: said light spot and said mirror being conjugate with respect to said cylindrical lens on said incident part, and said mirror and said recording point being conjugate with respect to said cylindrical lens on said reflected part.

2. In an impulse recording optical system, the combination of light beam defining means which include means for forming a light spot of vertically graded light flux; a. recording point past which a film may move in a substantially vertical direction; a mirror adapted to vibrate about a horizontal axis, said light beam being deflected by said mirror so as to have a part which is incident from said light spot upon said mirror, and a part which is reflected from said mirror towards said recording point; means placed between said light spot and said mirror for folding said incident part; and a cylindrical lens placed between said folding means and said mirror and between said mirror and said recording point, said cylindrical lens having its cylinder axis vertical and being traversed by said incident and reflected parts: said light spot and said mirror being conjugate with respect to said cylindrical lens on said incident part, and said mirror and said recording point being conjugate with respect to said cylindrical lens on said reflected part.

3. In an impulse recording optical system, the combinationof light beam defining means which include means for forming a light spot of vertically graded light flux; a recording point past 10 which a film may move in a substantially vertical direction; a mirror adapted to vibrate about a horizontal axis, said light beam being deflected by said mirror so as to have a part which is incident from said light spot upon said mirror, and a part which is reflected from said mirror towards said recording point; means placed be tween said light spot and said mirror for folding said incident part; means placed between said mirror and said recording point, and forming a horizontal slit; a cylindrical lens placed between said folding means and said mirror and between said mirror and said slit forming means, said cylindrical lens having its cylinder aXis vertical and being traversed by said incident and reflected parts; first imaging means placed in front of said mirror and acting in the vertical plane; and second imaging means placed between said slit forming means and said recording point and acting in only the vertical plane: said light spot and said mirror being conjugate with respect to said cylindrical lens on said incident part, said mirror and said recording point being conjugate with respect to said cylindrical lens on said reflected part, said light spot and said slit being conjugate with respect to said first imaging means, and said slit and said recording point being conjugate with respect to said second imaging means.

JOHN A. MAURER, JR.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,999,721 Dlmmick Apr. 30, 1935 2,095,317 Dimmick Oct. 12, 1937 2,121,568 Newcomer June 21, 1938 2,157,166 Dimmick May 9, 1939 

